Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface in a first embodiment showing my new design;

FIG. 2 is a front view of a display screen or portion thereof with a graphical user interface in a second embodiment shown on a smartphone;

FIG. 3 is a back view thereof;

FIG. 4 is a right-hand side view thereof;

FIG. 5 is a left-hand side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines showing a smartphone and the other broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or a portion thereof with a graphical user interface, as shown and described. 